This invention relates to a filter unit and associated assembly useful for removing contaminants such as water and particulate matter from fuel, especially diesel fuel. The invention is especially adapted for vacuum side (also called suction side) placement of the filter.
Numerous types of fuel filter separator units have heretofore been used to remove particulate and liquid (e.g., water) contaminants from fuel.
As used herein, "filter", "fuel filter", or "filter unit" shall include any device for separating particulate and/or liquid contaminants from fuel. Thus, fuel filter/separator units will be referred to simply as fuel filters or filter units.
The fuel filter as used with diesel engines may be placed on either the pressure side of the fuel pump or on the suction side of the fuel pump. When fuel passes through the fuel pump, any water in the fuel is usually broken down into very small or micro droplets. This emulsification of the water in the fuel makes it somewhat more difficult to separate the water from the fuel then would otherwise be the case. Accordingly, a suction or vacuum side filter may operate satisfactorily if it will separate out relatively large droplets of water, whereas a pressure side filter must be designed to separate out very small droplets of water.
A problem common to numerous prior art filter assemblies is their lack of flexibility. In particular, such assemblies often are limited to either vacuum side applications or pressure side application. A filter which is quite satisfactory for vacuum side applications may not function properly to separate out water which has been emulsified by passage through the pump in a pressure side application.
Assemblies which are designed to operate in pressure side application commonly have coalescing media in order to coalesce small water droplets into larger droplets. Such designs may include dual contaminant collection zones, one collection zone upstream from the coalescing media and a second collection zone downstream from the coalescing media. Coalescence and H.sub.2 O saturation may result in differential pressure across the wall separating these collection zones. These collection zones must be separated to avoid fluid bypassing the filter media across them. On the other hand, the isolation between the two collection zones is disadvantageous in a vacuum or suction side application where most of the contaminant settles on one side of the medium. Specifically, the isolation between the two collection zones limits the volume of contaminant collection to the reservoir in which most of the contaminant settles leaving the other partially or fully unused.
Although a coalescing filter may be used on the suction side of the fuel pump, its advantageous ability to remove smaller water droplets is generally unnecessary in such an application. Moreover, the use of a so-called quiet zone gap between a first coalescing filter media and a second filter media (as commonly used to allow water droplets to drop from the fuel) limits the capacity of the filter to hold dirt and, therefore, limits the life of the filter. Further, the extra cost (due to increased complexity) of a coalescing filter is not usually justified for suction side filter application.
In addition to lack of adaptability to both pressure and vacuum side applications, numerous prior art designs use contaminant collection zones which are hard to attach or remove.
Another problem common with fuel filter assemblies is that the filter elements become restricted too quickly. At the same time, attempts to design filter elements and assemblies for extended element life often result in complex and costly structures.